The two images below present one two-headed arrow that looks to be orange in color and another that appears to be red. In reality, the two are exactly the same color (red).

The only difference between the two is the color of the border that surrounds the red squares. The light yellow border used in the top figure gives the red square the appearance of being orange. Image by Brad Honeycutt, the co-author of The Art of the Illusion.